She is helpful to you only when it benefits her, she's playing the long game. While what you say about Jake is true, Ella nudged him into certain mindsets and actions, even posing as the MC to muddy the waters. Jake was a weak-minded pawn. While he is powerful, he's nowhere near as dangerous as she is.
She is well-written. But, she is still quite villainous.
Her willingness to kill you doesn't bother you?
I guess one reason I like her as a villain is she's extremely unique, and on top of that not an ntr antagonist. There's 3 ntr antagonists I recall so far; the asshole at the school, the guy who wants to pay for Amber and her sisters swimming lessons, the guy who wanted to marry Alice. Honestly, she stands out from most AVNs from that alone, but her ability to manipulate without threats is impressive.
We really can only speculate as to why she's doing what she's doing though. Just out of curiosity, if she was killing us out of necessity or her own survival, would that make you hate her less? I don't even think she considers the mc her enemy, I think she perceives us as a foodsource.
I guess it doesn't bother me that much because there's no explanation. And characters like Jake for instance, their reasons were shit. "I hate you because you suddenly said mean things to me." "I put you in prison because I thought it would convince Ella to cure Mia." "I mindcontrolled your friends and made them show me their tits because I was horny."
I mean it's true that Ella tricked him, but he's a bright guy. He could figure things out, in fact you can even make him realize he was tricked if you have high enough rp with him in prison.